Communication Device and Communication Method

1. A communication apparatus comprising: a receiver which, in operation, receives a control signal including first downlink control information that is common to a plurality of terminal apparatuses and second downlink control information that is directed to at least one specific terminal apparatus of the plurality of terminal apparatuses, the first downlink control information being mapped to one of a plurality of first mapping candidates that are included in a common search space, which is configured in a Physical Downlink Control Channel (PDCCH) region of a subframe, and the second downlink control information being mapped to one of a plurality of second mapping candidates that are included in a user-specific search space, which is configured in an extended Physical Downlink Control Channel (extended PDCCH) defined within a Physical Downlink Shared Channel (PDSCH) region of the subframe, and receives decoding area information that indicates whether the extended PDCCH should be decoded for each terminal apparatus; and a decoder which, in operation, according to the decoding area information, decodes each of the plurality of first mapping candidates in the PDCCH area or decodes each of the plurality of first mapping candidates in the PDCCH area and each of the plurality of second mapping candidates in the extended PDCCH to acquire the first downlink control information and the second downlink control information that is directed to the communication apparatus itself, wherein a number of the second mapping candidates included in the user-specific search space equals to or is more than a number of the first mapping candidates included in the common search space.

2. The communication apparatus according to claim 1 , wherein each of the plurality of first mapping candidates and each of the plurality of second mapping candidates are comprised of one control channel element (CCE) or a plurality of aggregated CCEs; the number of the first mapping candidates is a sum of numbers of mapping candidates, the numbers respectively corresponding to a plurality of CCE aggregation levels defined in the common search space; and the number of the second mapping candidates is a sum of numbers of mapping candidates, the numbers respectively corresponding to a plurality of CCE aggregation levels defined in the user-specific search space.

3. The communication apparatus according to claim 1 , wherein the CCE aggregation levels defined in the common search space are four and eight; and when the CCE aggregation levels is four, the number of mapping candidates is four; and when the CCE aggregation levels is eight, the number of mapping candidates is two.

4. The communication apparatus according to claim 1 , wherein a DM-RS is mapped as a reference signal to the extended PDCCH.

5. The communication apparatus according to claim 1 , wherein CRS is mapped in the common search space as a reference signal and DM-RS is mapped in the user-specific search space as the reference signal.

6. The communication apparatus according to claim 1 , wherein the decoder decodes each of the plurality of first mapping candidates and each of the plurality of second mapping candidates, for each of a plurality of DCI formats.

7. The communication apparatus according to claim 1 , wherein temporary C-RNTI is applied to the PDCCH region.

8. The communication apparatus according to claim 1 , wherein the decoder decodes each of the plurality of first mapping candidates and each of the plurality of second mapping candidates by using a terminal ID of the communication apparatus.

9. A communication method comprising: receiving a control signal including first downlink control information that is common to a plurality of terminal apparatuses and second downlink control information that is directed to at least one specific terminal apparatus of the plurality of terminal apparatuses, the first downlink control information being mapped to one of a plurality of first mapping candidates that are included in a common search space, which is configured in a Physical Downlink Control Channel (PDCCH) region of a subframe, and the second downlink control information being mapped to one of a plurality of second mapping candidates that are included in a user-specific search space, which is configured in an extended Physical Downlink Control Channel (extended PDCCH) defined in the Physical Downlink Shared Channel (PDSCH) region of the subframe, and receiving decoding area information that indicates whether the extended PDCCH should be decoded for each terminal apparatus; and according to the decoding area information, decoding each of the plurality of first mapping candidates in the PDCCH area or decoding each of the plurality of first mapping candidates in the PDCCH area and the plurality of second mapping candidates in the extended PDCCH to acquire the first downlink control information and the second downlink control information that is directed to the communication apparatus itself, wherein a number of the second mapping candidates included in the user-specific search space equals to or is more than a number of the first mapping candidates included in the common search space.

10. The communication method according to claim 9 , wherein each of the plurality of first mapping candidates and each of the plurality of second mapping candidates are comprised of one control channel element (CCE) or a plurality of aggregated CCEs; the number of the first mapping candidates is a sum of numbers of mapping candidates, the numbers respectively corresponding to a plurality of CCE aggregation levels defined in the common search space; and the number of the second mapping candidates is a sum of numbers of mapping candidates, the numbers respectively corresponding to a plurality of CCE aggregation levels defined in the user-specific search space.

11. The communication method according to claim 9 , wherein the CCE aggregation levels defined in the common search space are four and eight; and when the CCE aggregation levels is four, the number of mapping candidates is four; and when the CCE aggregation levels is eight, the number of mapping candidates is two.

12. The communication method according to claim 9 , wherein DM-RS is mapped as a reference signal to the extended PDCCH.

13. The communication method according to claim 9 , wherein CRS is mapped in the common search space as a reference signal and DM-RS is mapped in the user-specific search space as the reference signal.

14. The communication method according to claim 9 , wherein the decoding includes decoding each of the plurality of first mapping candidates and the plurality of second mapping candidates, for each of a plurality of DCI formats.

15. The communication method according to claim 9 , wherein temporary C-RNTI is applied to the PDCCH region.

16. The communication method according to claim 9 , wherein the decoding is performed by decoding each of the plurality of first mapping candidates and each of the plurality of second mapping candidates by using a terminal ID of the communication apparatus.